This invention relates to the technical field of thermal recording apparatuses that perform image recording with thermal recording materials containing a heat-reducing metallic compound such as silver behenate or the like.
Images taken for medical diagnosis by ultrasonography, computerized tomography (CT), magnetic resonance imaging (MRI) or radiography are conventionally recorded on silver salt photosensitive materials and used in various diagnoses as hard copies.
The silver salt photosensitive materials have the advantage of yielding high-quality images, but the development thereof is time-consuming and laborious because of the necessity of wet processing including color development, fixing-bleaching and rinsing. Maintenance of developing machines such as wet-type processors is also a time-consuming job. Therefore, it is desired that hard copies be outputted by an image forming method which eliminates the need for wet processing.
Thermal image recording is known as an image forming method that does not require wet processing. This recording system uses thermal recording materials that produce color by heating. The materials are heated imagewise in accordance with images to be recorded, thereby producing hard copies each having a visible image formed thereon. Image recording is usually performed by imagewise heating of the thermal recording materials with a light beam such as laser beam or a thermal head.
Thus, in thermal image recording in which a light beam is used to heat a thermal recording material and to form color thereon, the light beam emitted from a heat mode laser is modulated in accordance with an image to be recorded and deflected in a main scanning direction. The thermal recording material is heated imagewise by two-dimensional scanning with the light beam, while being held in a specified image recording position and being transported in the auxiliary scanning direction perpendicular to the main scanning direction, whereupon the image is recorded thereon.
On the other hand, thermal image recording uses a thermal head having a glaze in which heat-generating elements are arranged in one direction (i.e., main scanning direction). The respective heat-generating elements are heated in accordance with an image to be recorded, while moving the glaze and a thermal recording material relative to each other in the direction perpendicular to the main scanning direction, with the former pressed on the latter. The thermal recording material is thus heated imagewise.
In recent years, the quality of the image obtained by thermal recording has been significantly improved, and an extension of its use from the conventional ultrasonic imaging to other applications such as CT, MRI and radiography that require large and high-quality images is being reviewed.
Especially, thermal image recording with the heat mode laser can provide images of which the resolving power is as high as in image recording by light beam scan exposure on silver salt photosensitive materials.
A thermal recording material having an image forming layer that comprises a heat-reducing metallic compound such as an organic silver salt, a reducing agent thereof, a dye for infrared absorption and a toner, is known as one of the thermal recording materials utilized in such thermal image recording.
In this thermal recording material, metal in the heat-reducing metallic compound is reduced by heating to form an image and a latent image, which are then subjected to another heat treatment, whereupon a final image is obtained (see Unexamined Published Japanese Patent Application (Kokai) No. 179459/1996).
This type of thermal recording material is however low in sensitivity, which makes it difficult to obtain images having a sufficiently high quality, in applications which require high-quality images having high tone resolving power and resolution as in the aforementioned images for medical use.
In addition, the color tone of the image formed on the thermal recording material is brown, and the application thereof to the fields such as medical field in which black tone images are preferred because of their easy distinction of shadows, is disadvantageous.
The present invention has been accomplished under these circumstances and has an object of providing a thermal recording apparatus capable of performing a highly sensitive image recording using a thermal recording material having an image forming layer in which an image is formed with a heat-reducing metallic compound such as an organic silver salt, whereupon the resulting image has a black tone.
In order to achieve the above object, the present invention provides a thermal recording apparatus comprising:
pre-heating means for heating a thermal recording material on which an image is to be recorded, to a temperature 6 to 20xc2x0 C. lower than a color forming temperature;
heat recording means for recording the image by heating the pre-heated thermal recording material imagewise; and
post-heating means for heating the thermal recording material on which the image was recorded, to a temperature lower than the color forming temperature,
wherein said thermal recording apparatus uses the thermal recording material having a thermal image forming layer that comprises a heat-reducing metallic compound, and optionally at least one component selected from the group consisting of a reducing agent of said heat-reducing metallic compound, a dye for infrared absorption and a toner.
Preferably, the thermal recording means comprises one dimensional thermal recording means for recording thermally and one-dimensionally the image on the thermal recording material in a first direction and moving means for moving the thermal recording material relative to the one dimensional thermal recording means in a second direction perpendicular to the first direction, and thereby performing thermal image recording two-dimensionally on the thermal recording material.
Preferably, at least one of the pre-heating means and the post-heating means heats the thermal recording material in the first direction.
Preferably, at least one of the pre-heating means and the post-heating means comprises a heating light source extending in the first direction.
Preferably, the moving means is a scan transport means for transporting the thermal recording material in the second direction.
Preferably, the scan transport means comprises two transport roller pairs for transporting the thermal recording material in the second direction, and at least one roller of the two transport roller pairs has a heating source built in and functions as at least one of the pre-heating means and the post-heating means.
Preferably, the scan transport means comprises a platen roller for transporting the thermal recording material in the second direction and two transport rollers for nipping and transporting the thermal material between themselves and the platen roller, and at least one roller of the platen roller and the two transport rollers has a heating source built in and functions as at least one of the pre-heating means and the post-heating means.
Preferably, the one dimensional thermal recording means is a light beam scan optical system for deflecting and scanning a light beam in the first direction.
Preferably, the light beam scan optical system comprises modulation means for modulating the light beam in accordance with the image to be recorded using pulse width modulation, pulse number modulation or pulse amplitude modulation.
Preferably, the modulation means is a light source drive control means for modulating the light beam in accordance with the image to be recorded.
Preferably, the modulation means is an exterior modulator for modulating the light beam in accordance with the image to be recorded.
Preferably, the one dimensional thermal recording means is a thermal head having a plurality of heat generating elements for heating the heat-generating elements in accordance with the image to be recorded and extending in the first direction.
Preferably, imagewise heating of the heat-generating elements of the thermal head is controlled by pulse width modulation, pulse number modulation or pulse amplitude modulation in accordance with the image to be recorded.
Preferably, at least one of the pre-heating means and the post-heating means uniformly heats an entire surface of the thermal recording material.
Preferably, pre-heating by the pre-heating means is performed simultaneously with thermal image recording by the heat recording means.
Preferably, pre-heating by the pre-heating means is performed prior to thermal image recording by the heat recording means.
The pre-heating means heats the thermal recording material to a temperature preferably 10 to 18xc2x0 C., more preferably 14 to 16xc2x0 C. lower than a color forming temperature.
The post-heating means heats the thermal recording material to a temperature preferably 10 to 30xc2x0 C., more preferably 15 to 20xc2x0 C. lower than a color forming temperature.